Dental materials are used to manufacture artificial teeth, tooth parts or prosthetic plates. They contain, among other things, fillers, pigments, silane coupling agents, stabilizers and preformed polymerizates in addition to at least one polymerizable monomeric ester of methacrylic acid and one peroxidic catalyst which initiates the polymerization under heat.
The fillers are frequently microfine, inorganic materials with a particle size between approximately 0.01 and 5 .mu.m, especially silicon dioxide, but also mixtures of silicon dioxide with aluminum oxide, boric oxide, titanium dioxide or zirconium oxide. They can also be added at least partially into the dental material in such a manner that a polymer is prepared which consists essentially of esters of methacrylic acid, is cross-linked or non-cross-linked and contains the fillers, which are optionally surface-treated. If this filler-containing polymerizate is prepared as a granular or bead polymerizate, it can be added to the dental mass in this form and if it is prepared by bulk polymerization in compact form, then it is ground to a so-called sliver polymerizate. Other fillers are e.g. ground glasses or quartz with average particle sizes between approximately 1 and 10 .mu.m.
The pigments, added in a very small amount, have the function of adjusting the color of the dental material to correspond with the various shades of natural teeth or, in the case of dental plates, with the gum. Suitable pigments are e.g. iron oxide black, cadmium yellow and cadmium orange, zinc oxide and titanium dioxide.
Silane coupling agents are materials which comprise at least one polymerizable double bond for reaction with the monomeric esters of methacrylic acid. Their function is to improve the adhesion between the polymerizate and the fillers. Normally, the fillers are pretreated with these silane coupling agents and are used in this form. Suitable silane coupling agents are e.g. vinyl trichlorosilane, tris-(2-methoxyethoxy)-vinyl silane, tris-(acetoxy)-vinyl silane and 3-methacryoxypropyltrimethoxysilane.
Frequently used, preformed polymerizates are, in addition to the already-named granular polymerizates and sliver polymerizates containing fillers, homopolymerizates of methyl methacrylate or, preferably non-cross-linked copolymerizates of methyl methacrylate with a small amount of esters of methacrylic acid or acrylic acid with 2 to 12 carbon atoms in the alcohol component, advantageously in the form of a granular or bead polymerizate. Other suitable polymerizates are non-cross-linked products based on polyurethanes, polycarbonates, polyesters and polyethers.
Moreover, conventional dental materials also contain a monomeric ester of methacrylic acid, usually, however, a mixture of several such esters. Suitable monofunctional esters of methacrylic acid are e.g. methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-hexyl methacrylate and 2-hydroxy-ethyl methacrylate. Recently, however, polyfunctional esters of methacrylic acid have also been frequently used such as ethylene glycol dimethacrylate, butane diol-1,4-dimethacrylate, triethylene glycol dimethacrylate, dodecane diol-1,12-dimethacrylate, decane diol-1,10-dimethacrylate, 2,2-bis-[p-(.GAMMA.-methacryloxy-.beta.-hydroxypropoxy)-phenyl]-propane, the diadduct of hydroxyethyl methacrylate and trimethylhexamethylene diisocyanate, the diadduct of hydroxyethyl methacrylate and isophorone diisocyanate, trimethylol propane trimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate and 2,2-bis-[p-(.beta.-hydroxy-ethoxy)-phenyl]-propane dimethacrylate.
All these specified components can also be contained in the dental materials of the present invention, which therefore do not differ to this extent from known dental masses.
However, known, thermosetting dental masses contain a peroxide, especially dibenzoyl peroxide, which initiates the polymerization as a further essential component (cf. e.g. European Patent Application No. EP-A2-127 758). However, such dental masses containing dibenzoyl peroxide are not stable in storage to the degree desired. In particular, even brief, fairly sharp elevations of temperature, e.g. during storage in a warehouse, can result in an undesirable and premature polymerization. Therefore, refrigerated storage is prescribed as a general rule for such preparations. Moreover, dibenzoyl peroxide introduces the risk that the molded dental bodies produced from such known dental masses can exhibit clearly discernible discolorations after they have completely hardened.